This invention relates generally to vehicle simulators and more particularly to vehicle simulators having head-up displays.
It is known in the art to use vehicle simulators, such as aircraft flight or tank simulators, to train operators of such vehicles.
With respect especially to aircraft flight simulators, many aircraft, particularly fighter aircraft, have head-up displays which enable a pilot to view the outside environment in front of the aircraft together with information which is typically displayed on an instrument panel of the aircraft. The head-up display enables the pilot to observe a scene outside the aircraft (i.e., an “out-the-window” (OTW) scene) and at the same time to see, i.e., in superposition with the OTW scene, information (“symbology”), which the pilot may need, such as altitude, speed, a pointer to a target, etc.
An example of one such head-up display (HUD) is shown in FIG. 1 wherein a head-up display (HUD) optical system 10 projects information provided on the HUD's display device, such as a cathode ray tube (CRT) 12, to the eye 14 of an observer through an optical system 16. The optical system 16 is used to collimate the images (“symbology”), e.g., alphanumeric characters, lines, target pointers, etc.) produced on the HUD display device 12. The collimated HUD images are then viewed in superposition with the OTW imagery through the beamsplitter 18.
The HUD system 10 in the aircraft shown in FIG. 1 is focused at infinity (i.e., collimated) because the OTW scene being observed by the pilot is also typically at “infinity”. In the HUD system 10 shown in FIG. 1, if the pilot moves his head to the right, for example, not only does the target he is observing move to the right, but the symbology on the beamsplitter 18, such an example a pointer generated by the HUD 10 pointing to a target, also appears at the eye 14 to move to the right on the beamsplitter 18, thereby remaining on the target.
Referring to FIG. 2, a flight simulator 19 of the prior art is shown. The simulator 19 has the cockpit portion 21 of the aircraft, including has a HUD system 10. Simulator 19 includes a projector 24 driven by an image generator 26 to produce the simulated OTW scene, and the generated OTW scene is projected by the projector 24 onto a screen 28 for observation by the pilot being trained.
In the simulator, as in the real world, an acceptable superposition of the HUD and OTW imagery occurs when the two images are focused at the same distance. The screen 28, however, is not at infinity but relatively close to the eye 14 of the pilot, and consequently, the actual vehicle's HUD, which is focused at infinity for use in a real environment, cannot be used without modification.
One approach for making a HUD for such a simulator is to modify the optical system in the HUD 10 so that it focuses at the same distance from the eye 14 as the screen 28, i.e., such that the optical system 16 of the HUD 10 makes the symbology appear to the eye 14 as if it were located on the screen 28. The HUD optical system 16 must be modified so that a simulated, distant target being projected on the screen 28, and a symbology pointer (generated by the HUD 10) pointing to the target (which is generated on the OTW screen 28) appear co-located wherever the pilot in the simulator moves his head.
One problem with this design is that each different type of aircraft usually has a different HUD type, or multiple HUD types, and simulators for a given aircraft may use different displays forming images at differing distances from the user's eye. The optical system 16 for the HUD system 10 in the simulator 19 is a function of both the screen placement and the HUD type used in the simulator 19. A different optical system 16 must therefore be designed for each HUD type used with each different display having a different screen distance from the eye. Further, as refocusing requirements become shorter and shorter, to match decreased distances in the simulator's OTW display, it becomes more and more difficult to refocus the HUD optics while maintaining the actual HUDs FOV, vignetting characteristics, and mechanical packaging.
A technique to avoid this problem is to project the HUD symbology on the same screen on which the OTW scene is projected, as shown the simulator 19′ of FIG. 3. Both the OTW projector 24, which projects the OTW scene, and a HUD projector 30, which projects the HUD symbology, appear on the same screen 28, and consequently, the OTW scene and the symbology are physically co-located.
However, referring again to FIG. 1, in an actual cockpit environment, the HUD system 10 provides the symbology on only a limited portion of the field of view available to the pilot. If the pilot moves his head around in an actual cockpit as in FIG. 1, portions or all of the symbology may or may not be visible to the pilot due to optical limitations of the HUD system, herein described as occulting or vignetting. The term “occulting” is meant to broadly describe any blocking or interruption in the visibility of the symbology, such as by structures of the cockpit or in the HUD optical system. The term “vignetting” refers to a type of occulting which is caused by movement of the viewer's eye beyond the optically functional portions of the lens system which is normally in the center of the lens or lenses. The occulting or vignetting is caused by a combination of things in the HUD optical system 10, i.e., the beamsplitter 18, the lenses and lens frames of the optics, and the CRT. For example, if the pilot's head is moved so that some of the HUD FOV falls outside of the beamsplitter coverage 18, that portion is no longer viewable by the pilot.
Consequently, in the arrangement shown in FIG. 3, while projection of the HUD generated symbology and the OTW scene onto a common screen 28 produces the desired co-location effect, the system does not simulate the vignetting or occulting characteristics associated with the real HUD being simulated. The prior art therefore fails to provide a realistic simulation of a vehicle heads up display.